Electric furnace.



No. 718,892. PATENTED JAN.` 2o, 1903.

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APPLIUATION FILED DB0. zo, 1900. Y

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UNITED STATE-s MEN/Lilli@ EDWARD GOODRICH ACHESON, OF NIAGARA FALLS, NEWYOttis..

ELECTRIC FURNACE.'

SPECIFICATION forming' part of Letters :Patent No. 718,892, datedJanuary 20, 1903. Application filed December 20, 1900.V Serial No.40,516. (No model.)

To all whom, it ntcty concern:

Be it known that I, EDWARD GOODRICH ACHESON, of Niagara Falls, in thecounty of Niagara and State of New York, have invented a new and usefulImprovement in Electric Furnaces, of which the following is a full,clear, and exact description, reference being had to the accompanyingdrawings, forming part of this speciiication, in which- Figure 1 showsin vertical longitudinal section an electric furnace constructed inaccordance with myinvention. Fig. 2 is a similar View showing thefurnace at the end of the operation. Fig. 3 is a vertical cross-sectionon the line III III of Fig. l. Fig. 4 is a vertical cross-section on theline IV IV of Fig. 2.

My invention relates to an electric furnace so constructed that thematerials to be treated therein may be subjected to heat without anydisturbing chemical influence being exerted upon them by the conductorthrough which the current passes and in which the heat is generated.Such conductors are usually made of carbon, and the affinity of carbonfor other elements has hitherto served to prevent the use of electricfurnaces for the performance of any of the reactions for which itotherwise would be well adapted.

In constructing my furnace I take a conductor, preferably of carbon, andplace between it and the material to be treated a protecting layer orsheath composed of a refractory carbid, which is preferably preformedand placed around the conductor, or it may be created in the furnace atthe outset of the process, and having thus protected the conductor fromcontact with the material to be treated I raise the conductor to a hightemperature by the passage of an electric current and heat the materialto be treated by conduction or radiation therefrom. The material to betreated may consist of a mixture of metallic oxid or compound with areducing agent, preferably carbon, and being shielded from the core isnot affected thereby to any injurious extent, or the furnace may be usedsimply for melting materials, such as silica or other compounds ormetals. The material to be heated is necessarily different iningredients or proportions from the protecting layer of carbid, as vwillbe more fully set forth.

Referring now to the drawings, I will describe my furnace in its bestform prepared forr use in the reduction of metallic aluminium fromalumina.

In the drawings, Fig. l, 2 represents the walls of an electric furnace.

3 3 are the terminals of the dynamo-circuit.

4 is the carbon conductor or core which connects the terminals and is ormay be constituted of granular coke, though rods or plates of carbon maybe employed.

5 is the body 0f charge mixture which surrounds the conductor and iscomposed of the oxid to be reduced mixed with powdered carbon inchemical proportion suitable for reduction.

Between the body of material to be heated and the conductor 4 is ashield or layer 8, composed either of preformed refractory carbid or ofthe materials which when combined will form a carbid. Thus the shieldmay consist of crushed crystals of carbid of silicon or carbid of boronplaced around the conductor,

or it may consist of sand or boracic acid and carbon mixed together inproper proportion to form carbid of silicon or carbid of boron, or theseoxids and carbon in less proportion may be placed in intimate contactwith the core and converted into carbid during the first stages of theprocess by combining with a portion of the carbon of the core. When heatis passed through this conductor, its first effect is to heat the shield8, and if it consists of the preformed carbid to cause it to adhere intoa dense mass, or if it is composed of materials adapted to combine as acarbid, the heat will cause such combination to take place, and ineither case the conductor will be protected from contact with the chargeby the intervening layer or shield, the heatwhich is generated in theconductor being transmitted through such shield to the charge mixture.When the charge mixture consists of silica and carbon, they will reactand will liberate metallic aluminium, which will co1- lect in a moltenmass 6, Fig. 2, at the bottom of the cavity 7 which the reductioncreates, and the carbid shield 8 will be rendered sufficiently strongand dense to uphold the con- IOO ductor even if the latter is made ofgranular carbon.

The electric current which I employ may be alternating or direct and ofa current density of, say, thirty am peres or more per square inch ofcross-section of core when the core is granular and of greater currentdensity when the core is made of rods or plates. Care should be takennot to use a current density great enough to generate such a high degreeof heat as to decompose the carbid shield.

During the process the charge mixture is protected from the core, whichis thereby prevented from interfering with the reactions which aredesired.

The preferable form of my furnace is that in which the conductor isshielded byalayer of preformed carbid, because such layer is caused bythe heat to cohere in a dense mass of good heat conductivity, throughwhich the heat is readily transmitted and which thoroughlyprotects theconductorfrom the charge. I therefore intend to make specific claimthereto. It will be understood, however, that Within the scope of myinvention as broadly claimed the furnace may be modified inconstruction--a tube of carbid which has already been formed and filledwith carbid may be used in building the furnace-and that it is notnecessary the carbid layer or shield should completely surround theconductor, it being necessary' only that it should be so arranged as toprotect' the conductor from contact with the charge.

The incandescent furnace is in many respects the most efficient,easily-handled, and all-around useful design for electric heating; butit has heretofore been seriously limited by the reactions that takeplace between the conducting-core and the materials being operated upon.Efforts have been made to overcome this difculty by interposingprotecting-coatings, and for this purpose clay, corundum, and otherhighly-refractory materials have been used and found more or lessefficient Where the temperatures were not sufficient to cause themelting of the material of which they were formed or, as sometimesoccurs, their reduction Where they are in contact with the carbonconducting-core. Another difculty that inventors have sought to overcomeis the tendency of the current to leave the properly-preparedconducting-core and pass through the materials being operated upon wherethey form more or less of a conducting mass. To correct this difficulty,various materials have been suggested, such as clay, oxids, and in someinstances iinelypowdered carbon or charcoal on account of theirrelatively high resistance quality, as is suggested by Elihu Thomson inhis Patent No. 513,602. All of these attempts have been more or lesssuccessful, but have not met the conditions as met by my discovery thatcarbid of silicon might be used for the double purpose of preventingchemical reaction between the carbon core and the charge of the furnace,and also largely assist in insulating the surrounding'charge in orderthat the current might be more thoroughly conned to the preparedconducting-core. Oarbid of silicon is stable at the highest temperaturesordinarily desired for metallurgical operations, and the silicon beingalready thoroughly satisiied no reaction occurs between it and the conducting-core. I have also discovered that itis inert at high temperatureswhile in contact with many materials it is desired to reduce, melt, orsmelt in the electric furnace.

I claiml. An electric furnace having a carbon electrical conductor witha protecting-layer of refractory carbid and having electricalconnections at the ends of the conductor; substantially as described.

2. An electric furnace having an electrical conductor, and aprotecting-layer of preformed refractory carbid in contact therewith,said conductor having electrical connec tions at its ends; substantiallyas described.

An electric furnace having an electrical conductor and `aprotecting-layer of refractory carbid, said carbid layer being placedaround the conductor and surrounded by a space for;` the reception ofmaterial to be treated and the conductor having electrical connectionsat its ends; substantially as described.

In testimony whereof I have hereunto set my hand.

EDWARD GOODRIGII ACIIESON. Witnesses:

G. I. HoLDsHIP, GEO. B. BLEMING.

